1. Field of the Invention
The present invention relates to a pump equipment having one or more rotary pumps and a method for assembling the pump equipment. In particular, the present invention is preferably applied to an internal gear pump such as a trochoid pump or the like for brake apparatus for vehicles.
2. Description of Related Art
A rotary pump, for example, an internal gear pump, is comprised of a drive shaft to be driven by a motor, an inner rotor and an outer rotor to be rotated by the drive shaft and a casing for containing the drive shaft and the inner and outer rotors. The casing is provided with a pump room in which the inner and outer rotors are contained, an intake port and a discharge port for sucking and discharging oil and a shaft hole communicating to the pump room from the motor side. The drive shaft is fitted into the inner rotor through the shaft hole. In case of the internal gear pump, an oil leakage from a clearance between the casing and the drive shaft tends to be caused as its nature. To prevent the oil leakage from the clearance between the casing and the drive shaft to outside, an oil seal is provided to fill in the clearance, as described in JP-A-SHO-118977.
On the other hand, as plenty of areas at both side surfaces of the inner and outer rotors contact an inner wall of the pump room in the casing, there is a fear that the inner rotor may seizure with the inner wall of the pump room due to the lack of lubricant oil. The area of the side surfaces of the inner and outer rotors to be exposed to the intake and discharge ports is sufficiently lubricated by oil to be sucked and to be discharged. Further, the area outside in a diameter direction from the intake and discharge ports is also well lubricated due to oil running on the contacting surface by a centrifugal force to be induced, when the inner and outer rotors are rotated. However, the area inside in a diameter direction from the intake and discharge ports, in particular, at the intake port side, is not sufficiently lubricated because of no effect of the centrifugal force. Further, in the case of the rotary pump in which the drive shaft is held by one or more bearings disposed in the shaft hole of the casing, there is a possibility that the bearing seizure takes place because the relatively slender size of bearings are generally used and tend to be filled with heat.
Furthermore, as an example of the pump in which two rotary pumps are rotated by a drive shaft, a tandem pump equipment is described in JP-A-H.9-126157. In the tandem pump equipment, the discharge ports of the two rotary pumps are provided, respectively, in the same direction from the drive shaft and the intake ports, respectively, in the same direction from the drive shaft, but in the opposite direction from the respective discharge ports. Each pressure at the respective discharge ports of the two rotary pumps is reacted in the same direction against the drive shaft and the drive shaft receives an unbalanced force so that the pump operation may be adversely affected due to the bending of the shaft.
An object of the present invention is to provide rotary type pump equipment having a construction that the intake port is positively communicated, inside the oil seal of the casing, with the shaft hole for inserting the drive shaft for the purpose of lubrication. This construction is effective not only for smoothly rotating the drive shaft and the pump, but also for easily escaping air entered through the oil seal from the intake port.
More clearly, it is an aspect of the present invention to provide a rotary pump in which the seizure will not happen at the side surfaces of the inner rotor. There is provided a fluid groove extending from the intake port to the center bore in both inner surfaces of the pump room in the casing, respectively. When the rotors are rotated, fluid oil is supplied from the fluid groove to a small gap between the inner surface of the pump room and the side surfaces of the rotors. The fluid will serve, as lubricating oil, to prevent the seizure of rotors. Further, a fluid path along the drive shaft is provided on the inner surface of the center bore of the casing for communicating the fluid groove to an intake conduit which transmits fluid to the intake port of the pump room. A part of the fluid path is constituted through the portion where the bearing for holding the drive shaft is located on the surface of the shaft hole of the casing. The flow of fluid through the intake conduit, the bearing portion, the fluid path along the drive shaft, the fluid groove and the intake port of the pump room will serve to prevent the seizure of the rotors as well as the seizure of the bearing.
On the other hand, it is important to prevent the fluid leakage from the discharge port to the intake port as much as possible for improving a pump efficiency. For this purpose, the inner surface of the pump room, that is, the surfaces of cylinders constituting the pump room, is fabricated by grinding in the direction not crossing the intake port and the discharge port.
In case of applying the pump equipment mentioned above to the brake apparatus, it is preferable that the intake port of the pump is disposed at a portion of the hydraulic circuit where the fluid pressure is relatively low. To prevent the high pressure to be applied to the intake port, there is generally provided, at an intake port side of the pump in the hydraulic circuit, with a control valve for controlling the communication and interruption of the fluid conduit or a low pressure reservoir with a pressure regulating valve at its intake side. However, if high pressure is applied accidentally to the intake port due to a malfunction of the control valve or the reservoir, there is a fear that oil is leaked to the outside through the above oil seal or the oil seal is broken down, as the case may be.
Therefore, it is another aspect of the present invention to provide a rotary type pump equipment capable of preventing fluid leakage to the outside, even if high pressure is applied to the intake port. For this purpose, in addition to a first seal, a second oil seal for filling the clearance between the drive shaft and the shaft hole of the casing is disposed at an opposite side of the pump room adjacent to the first oil seal.
In particular, it is preferable to provide a communicating conduit between the first and second oil seals in order to transmit the fluid leaked from the clearance between the drive shaft and the first oil seal to a relatively low pressure fluid conduit of the hydraulic circuit.
A further aspect of this invention is to provide pump equipment having one or more rotary pumps, in which the drive shaft of the pump is coupled with a motor shaft of the motor inside a motor bearing so as to rotate smoothly the drive shaft, even if the center axes of the motor shaft and the drive shaft are offset. The back up plate for the oil seal of the pump side is commonly used for fixing the motor shaft bearing. Therefore, the number of the components constituting the pump equipment is so far reduced.
Furthermore, it is possible to provide a fluid communicating path between the oil seal of the pump side and the motor bearing. For this purpose, the back up plate is provided with a fluid path such as a groove for guiding fluid leaked through the oil seal of the drive shaft to the low pressure conduit so that the fluid may be prevented from going into the motor.
A further object of the present invention is to provide pump equipment having two rotary pumps to be rotated by a drive shaft in which fluid leakage through the shaft hole of the casing, for example, between the two pumps or between the pump and the motor, may be reliably prevented. A sealing member constituted by a ring shaped resin element and an elastic ring element fitted into the groove of the resin element is installed in the shaft hole of the casing. As the elastic ring element is positioned in the groove of the resin element, the accurate position of the elastic ring element may be always secured so as to ensure oil sealing effect and, if applied between the two pumps, the elastic ring element will not be worn by the friction with the pump rotor.
A further aspect of the present invention is to provide a pump equipment having a plurality of rotary pumps capable of smoothly rotating the pumps because of a limited bending of their drive shafts. The pump equipment has a construction that the respective discharge ports of the rotary pumps are located at the points which are nearly symmetrical with respect to the center axis of the drive shaft. The respective reaction forces against the drive shaft to be produced by the high pressure at the respective discharge ports may counterbalance each other so that the possible bending of the drive shaft may be limited. As another aspect of the present invention for limiting the bending of the drive shaft for the pump equipment having two rotary pumps, the intake and discharge fluid conduits of one pump and the intake and discharge fluid conduits of the other pump are arranged at the locations which are not between the pumps, but outside from the pumps, respectively. Preferably, the respective discharge fluid conduits of the two pumps are located at the points which are opposite each other, more preferably, different at an angle of 180 degrees each other, with respect to the center axis of the drive shaft. These locations of the intake and discharge fluid conduits will serve to narrow the space between the two pumps so that the pump equipment may become compact.
As a further aspect of the present invention, two bearings for holding the drive shaft are arranged outside the two pumps, that is, at the respective positions between which the two pumps are inserted. The forces due to the high pressure at the discharge ports are reacted against the drive shaft inside the two bearings. Therefore, the bending of the drive shaft is more limited, compared with a case that the forces are reacted against the drive shaft outside the two bearings.
Furthermore, it is one of the objects to provide a method for assembling the pump equipment in such a way that a part of the peripheral border between respective cylindrical members, which can be stacked on top of another and fixed together for constituting the casing, is tentatively welded first by a laser beam and, then, is finally welded all around the respective peripheral borders. Such a method is effective for limiting a deformation or a position shift of the respective members, because the energy of the tentative spot welding by laser beam is less than that of the final welding and, therefore, the deformation force by laser beam is not so strongly influenced.
It is preferable to apply to the welding portions the laser beams from plural side positions at the same time so as to counterbalance each other the respective forces given by laser beams to the welding portions. This method may be used in the above tentative spot welding. Furthermore, such a method makes it possible to weld all around the peripheral borders without causing the deformation or the position shift of the respective cylindrical members, even if the tentative spot welding is eliminated and the relatively large energy of laser beams is applied at the same time to the welding portions.
It is a final object of the present invention to provide a brake apparatus having a hydraulic circuit in which the pump equipment described above is applied. The pump equipment is used for increasing fluid pressure to wheel cylinders in the hydraulic circuit. In particular, each plural rotary pump is operative in each of the fluid conduits separately provided in the hydraulic circuit.